1. Field of the Invention
The present invention relates to a call control method between a packet network and public switched telephone networks (PSTNs) in the next generation network and more particularly to a method, for networking between a packet network and PSTNs in the next generation network, which may enable a terminating media gateway controller to conduct the virtual continuity (COT) check when processing ISDN user part (ISUP) calls.
2. Background of the Related Art
As illustrated in FIG. 1, the next generation network in the related art comprises a packet network (10), media gateways (21, 22), media gateway controllers (31, 32), signalling gateways (41, 42), and PSTNs (51, 52).
In the next generation network described above, the packet network (10) and the PSINs (51, 52) may be interfaced by the media gateways (21, 22) and the media gateway controllers (31, 32). There are various types of the media gateways (21, 22) corresponding to the types of media and the media gateways (21, 22) are operated by the control of the media gateway controllers (31, 32).
In order to control the packet network (10) consistently without regard to types of the bearer for voice or other data, the call control signalling and the bearer control signalling for voice or other data control must be distinguished.
In other words, if a call is made from the originating PSTN (51) to the terminating PSTN (52), the call control signalling is transferred from the originating PSTN (51) to the originating signalling gateway (41), to the originating media gateway controller (31), to the terminating media gateway controller (32), to the terminating signalling gateway (42), and then to the terminating PSTN (52), while the bearer control signalling for voice or data is transmitted from the originating PSTN (51) to the originating media gateway (21), to the packet network (10), to the terminating media gateway (22) and then to the terminating PSTN (52).
The call control protocol between the media gateway controllers (31, 32) is Bearer Independent Call Control (BICC) protocol or Session Initiation Protocol-Telephone (SIP-T) protocol, or the like. The call control protocol between the packet network (10) and the PSTNs (51, 52) (i.e., the call control protocol between the media gateway controllers (31, 32) and the PSTNs (51, 52)) is ISUP protocol. For the convenience of illustration, the call control protocol between the media gateway controllers (31, 32) will be assumed to be BICC protocol in the following.
The call control signalling between the originating PSTN (51) and the terminating PSTN (52) is conducted as follows.
First, the originating PSTN (51), using the ISUP signaling, makes the call requested by an originating subscriber transmitted through the originating signalling gateway (41) to the originating media gateway controller (31) which controls the originating signalling gateway (41), in order to make the call go through the packet network (10).
Then, the originating media gateway controller (31) translates a called number and searches for and finds the corresponding terminating media gateway controller (32). BICC, SIP-T, or the like may be used for the signalling between the originating media gateway controller (31) and the terminating media gateway controller (32).
Through the number translation, the terminating media gateway controller (32) searches for and finds the terminating PSTN (52). For the processing of the call to the located terminating PSTN (52), the call is transmitted through the terminating signalling gateway (42) to the terminating PSTN (52) by ISUP signaling.
On the other hand the bearer control signalling between the originating PSTN (51) and the terminating PSTN (52) is conducted as follows.
First, a bearer data of the originating PSTN (51) is transmitted to the originating media gateway (21) via a trunk. The originating media gateway (21) commences the signalling to send the bearer data to the packet network (10) according to the control of the originating media gateway controller (31).
Then, the terminating media gateway (22) receives the bearer control signalling from the packet network (10) according to the control of the terminating media gateway controller (32) and connects channels for the bearer connection. Also, the terminating media gateway (22) connects the trunk for the bearer connection to the terminating PSTN (52) upon receiving the control of the terminating media gateway controller (32).
Now, the call control inter-operation procedures between the packet network (10) and the PSTNs (51, 52) are explained with references to FIG. 2. There are two different kinds of call control procedures depending on the types of networks.
In the first kind of call control procedures, the originating media gateway controller (31) receives Initial Address Message (DIW, which is a call request message, from the originating PSTN (51) through the originating signalling gateway (41) so that the originating media gateway (21) may reserve the bearer information related to the call.
The originating media gateway controller (31) conducts the number translation of the DAM received through the originating signalling gateway and searches for and finds the corresponding terminating media gateway controller (32). Then, the originating media gateway controller (31) transmits the IAM to the located terminating media gateway controller (32).
The terminating media gateway controller (32), upon receiving the IAM from the originating media gateway controller (31), conducts the number translation of the called number, determines the trunk connecting the terminating media gateway (22) and the terminating PSTN (52), and notifies the terminating media gateway (22) of the trunk line reservation.
At this first time (the time indicated as ‘T1’ in FIG. 2) when the terminating media gateway controller (32) receives the IAM from the originating media gateway controller (31), the terminating media gateway controller (32) transmits the received IAM to the terminating PSTN (52) through the terminating signalling gateway (42).
The terminating media gateway controller (32) transmits the information concerning the terminating media gateway (22) and the bearer, contained in Application Transport Mechanism (APM) message, to the originating media gateway controller (31).
Then, the originating media gateway controller (31) sends a request for the bearer set-up to the originating media gateway (21), together with the information contained in the APM message received from the terminating media gateway controller (32).
The originating media gateway (21) conducts the bearer connection set-up by sending Bearer Set-up Request Message (BSRM) to the terminating media gateway (22). Thereafter, the originating media gateway (21) notifies the originating media gateway controller (31) of whether the bearer set-up is completed or not. The terminating media gateway (22) notifies the terminating media gateway controller (32) of the completion of the bearer connection set-up.
Thereafter, the call processing operation is conducted in the same manner as in the ordinary ISUP call processing.
On the other hand, in the second kind of call control procedures, as with the above-described operations, the terminating media gateway controller (32) notifies the terminating media gateway (22) of the trunk line reservation. Then, the information concerning the terminating media gateway (22) and the bearer, contained in an APM message, is transmitted to the originating media gateway controller (31).
Then, the originating media gateway controller (31) sends a request for the bearer set-up to the originating media gateway (21), together with the information contained in the APM message received from the terminating media gateway controller (32).
The originating media gateway (21) conducts the bearer connection set-up by sending a BSRM to the terminating media gateway (22). Thereafter, the originating media gateway (21) notifies the originating media gateway controller (31) of whether the bearer set-up is completed or not. The terminating media gateway (22) notifies the terminating media gateway controller (32) of the completion of the bearer connection set-up.
At this second time (the time indicated as ‘T2’ in FIG. 2) when the bearer connection set-up is completed, the terminating media gateway controller (32) transmits the IAM received from the originating media gateway controller (31) to the terminating PSTN (52) through the terminating signalling gateway (42).
Thereafter, the call processing operation is conducted in the same manner as in the ordinary ISUP call processing.
In both of the two kinds of the related art described above, there exist problems caused by the difference between the first time (T1) when the terminating media gateway controller (32) receives the IAM from the originating media gateway controller (31) and the second time (T2) when the bearer connection set-up is completed.
In the case of the first kind described above, because the initial IAM is transmitted to the terminating PSTN (52) while the packet network (10)'s bearer connection is not yet completed, a call request at the terminating end may be made to a terminating subscriber even when the bearer connection is not made. In other words, even if the terminating subscriber heard the ring or is holding the receiver, the subscribers may not hear any sound until the bearer is connected. Also, if the bearer connection fails in the packet network (10), the call may be terminated irregularly.
In the case of the second kind described above, because the initial IAM is transmitted at the time when the bearer connection is completed, the problem of the first kind may be avoided. However, when the terminating media gateway controller (32) receives the IAM from the originating media gateway controller (31), the trunk between the packet network (10) and the terminating PSTN (52) is merely reserved and the initial IAM is not sent until the bearer connection set-up is completed. Thus, there occurs a problem of dual seizure of the trunk. In other words, because the terminating PSTN (52) may not recognize trunks reserved in advance by the terminating media gateway controller (32), the call connection may frequently fail due to the dual seizure of the trunk.
As described above, in the call control method between the packet network and the PSTN in the next generation network in the related art, because the media gateway controller seizes the trunk between the media gateway and the PSTN and transmits the initial IAM while the bearer connection between the media gateways is not completed, the call request may be made to the terminating subscriber even without the bearer connection. Also, if the bearer connection fails in a core network such as the packet network after the call receiver heard the ring or held the receiver, the call may have to be terminated irregularly. Furthermore, in the case where the initial IAM is sent after the bearer connection set-up is completed, because the trunk between the media gateway and the PSTN is seized in advance at the time when the terminating media gateway controller receives an IAM from the originating media gateway controller and because the initial IAM is sent only after the bearer connection set-up is completed, the problem of dual seizure of the trunk may occur.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.